In related art, as a connection structure for connecting a flexible printed circuit board (FPC board) made of a thermoplastic resin to a mother board, for example the connection structure disclosed in JP-A-2001-111209 is known. This connection structure is obtained in the following way.
That is, as shown in FIG. 11, respective connection terminal parts (lands) 113a, 111a of interconnection patterns 113 formed on an FPC board 105 and interconnection patterns 111 formed on a mother board 102 are brought together with solder paste 120a, 120b therebetween. Then, by means of a thermocompression tool 121, connecting areas of the boards 102, 105 are heated to above the glass transition point of the thermoplastic resin constituting the insulating layer 112 of the FPC board 105, and also a pressure is applied to them. As a result, the FPC board 105 and the mother board 102 are connected by the respective interconnection patterns 111, 113 being electrically connected by the solder and the thermoplastic resin constituting the insulating layer 112 of the FPC board 105 softening and becoming intimate with the insulating layer 110 of the mother board 102.
In the connection structure described above, the number of signal lines connected between the two boards is limited by the width of the FPC board 105 and the spacing of the interconnection patterns 113 including the lands 113a. Because of this, to increase the number of connecting signal lines it is necessary either to increase the width of the FPC board 105 or to make the spacing of the interconnection patterns 113 including the lands 113a as narrow as possible.
However, because of a requirement for small size and light weight, it is not possible to freely increase the width of the FPC board 105. And also with regard to narrowing the spacing of the interconnection patterns 113 including the lands 113a, because of problems such as migration and short-circuiting, and problems of etching precision at the time of formation of the interconnection patterns 113, it is not possible to greatly increase the number of connecting signal lines.
The present invention was made in view of these problems with related art, and an object of the invention is to provide a circuit board and a circuit board connection structure with which it is possible to greatly increase the number of connecting signal lines without increasing the width of the board parts being connected.